1. Field of the Invention
The present invention relates to wireless communication and, more particularly, to a method for re-selecting a cell in a wireless communication system and an apparatus therefor.
2. Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
A micro-cell, a femto cell, a pico cell, or the like, having a small service area may be installed at a particular location of a macro-cell having wide coverage. This is called a heterogeneous network.
A user equipment (UE) represented by a mobile device moves, so a cell that degrades quality of a currently provided service or a cell that provides a better service may be discovered. Due to this issue, a UE may move to a new cell, which is called conducting of UE mobility.
In order to conduct mobility, a UE continuously perform measurement on a serving cell and an adjacent cell. When measurement results satisfy conditions for conducting mobility, the UE may receive an instruction from the serving cell or may directly conduct mobility.
A particular type of cell may provide a particular service or permit only a particular subscriber to access, and provide a service. In this case, a UE may maintain connection to a cell that provides a corresponding service or a cell that allows for accessing, thus being provided with an enhanced service. To this end, cell re-selection priority of a particular cell may be adjusted to induce a UE to access a corresponding cell or limit UE accessing. For example, an autonomous priority handling technique may be used.
When UEs are induced to access a particular cell or limit UE accessing to a particular cell through adjustment of priority such as autonomous priority handling, UEs may access some of cells through cell re-selection, and in this case, the number of UEs which have accessed some cells may be overloaded, possibly causing a problem in terms of optimization of a network environment. Thus, a cell re-selection method for enhancing and optimizing network performance is required.